Three-dimensional CAD drawings are solid views which have several advantages over two-dimensional CAD drawings in that contours of product shapes can be recognized at a glance and product shapes can be easily understood.
Conventionally, the following labor-intensive work has been performed out to convert two-dimensional CAD drawings drawn isometrically to three-dimensional CAD drawings.
(1) Print a two-dimensional CAD drawing with dimensions that has been previously entered.
(2) Pick-up the dimensions from the printed two-dimensional CAD drawing by hand.
(3) Ridges and peaks relating to the dimensions that have been picked up are then inputted by hand onto three-dimensional axes of a grid drawn onto a monitor connected to the CAD system. Spline interpolation is then carried out with respect to a curved plane.
Three-dimensional CAD data corresponding to the two-dimensional CAD drawings is then obtained by drawing three-dimensional CAD drawings (solids) on the monitor using the aforementioned procedure.
In another conventional method, three-dimensional shapes of products are completed by inputting two-dimensional CAD drawings to planes in three dimensions and performing a transition in the third dimension direction.
However, in this conventional method of converting to a three-dimensional CAD drawing, the dimensions are read-in by inspection and a method of working where inputting is carried out by designating ridges and peaks corresponding to the read-in dimensions on a screen using a pointing device (coordinate input device such as a mouse etc.) is performed. Therefore, even in the case of a simple part such as a part for a motorcycle, the time required for inputting this information to construct a three-dimensional CAD drawing from a two dimensional CAD drawing is substantial. Furthermore, it is necessary to consider the likelihood of input mistakes and their effect on the three-dimensional drawing. Also, there are a large number of processes to make such a three-dimensional CAD drawing. The practical result is that three-dimensional CAD drawings can only be obtained for a limited number of products.
Therefore, in the related art, a three-dimensional figure data generating method has been proposed (for example, refer to Japanese Patent Laid-open Publication No. Hei. 6-60153) capable of automatically generating a solid model realizing the three-dimensional shape of an object from two-dimensional CAD drawings drawn in three planes.
This conventional method of generating three-dimensional figure data is suitable for generating three-dimensional figure data based on, for example, two-dimensional figure data relating to an orthogonal XYZ coordinate system, i.e. data relating to plane shapes of objects, data relating to front shapes of objects or data relating to side shapes of objects. However, in the case where figure data relating to planes of other coordinate systems, for example, figure data relating to planes taking an axis at a position that is skewed with respect to the orthogonal XYZ axes or figure data relating to partially projected views (section views) where an object is viewed from an arbitrary direction is included, concave closed loop processes or assistance line processing and concealed line processing becomes difficult, with further complications resulting from the bulkiness of attribute information are also possible.
The input work for this kind of conversion to a three-dimensional CAD drawing is inefficient. Furthermore, the amount of work for the CAD operators and the operation processing steps in the program are constantly increasing. Therefore, when servicing the working environment and system maintenance etc. are considered, there is a demand for a three-dimensional CAD system and a method for converting two-dimensional CAD drawings to three-dimensional CAD drawings capable of both alleviating the amount of work for the operators and shortening the operation time as well as reducing the operation processing steps of the program regardless of the kind of two-dimensional figure data.